Cancellation of Under construction Property

Dear Learned members, I have booked a flat in Mumbai in year 2015 and as per agreement the possession was due by June 2016. Builders have delayed the possession and they are now offering us fit out possession mentioning OC is expected by Dec 2018. we have paid 95% of the amount + stamp duty + registration + Service Tax + VAT till date. All above amounts were paid in July 2015. The agreement provides us to cancel if the possession is delayed beyond Jun 2016 and builders will pay interest @ 9% p.a. on amount paid. I am now looking to cancel the booking due to this delay. I am looking for advice On: 1. Can we cancel the agreement now even though 95% amount is being paid? 2. What is the process to initiate cancellation? 3. Within how much time builder is supposed to pay back the amount + interest to us? 4. If builder does not pay in this stipulated time then what are the remedies with us? 5. Can we claim for refund of stamp duty, registration charges, service tax & VAT paid? 6. If we decide NOT to cancel then what will be the GST that we have to pay on balance amount? Do let me know if you need any other details? Thanks in advance Best regards, Nilesh